It’s a basic necessity of life, as important to our health and well-being as air, food and water. When we sleep well, we wake up feeling refreshed, alert and ready to face daily challenges. When we don’t, every part of our lives can suffer. Our jobs, relationships, productivity, health and safety (and that of those around us) are all put at risk.
Sleep architecture follows a pattern of alternating: REM (rapid eye movement) and NREM (non-rapid eye movement) sleep throughout a typical night in a cycle that repeats itself about every 90 minutes. As we begin to fall asleep, we enter NREM sleep (75% night) which is composed of stages 1-4
Stage 1
- Light Sleep, between being awake and falling asleep
Stage 2
- Onset of sleep and becoming disengaged from surroundings
- Breathing and heart rate are regular
- Body temperature drops (so sleeping in a cool room is helpful)
Stages 3 & 4
- Deepest and most restorative sleep
- Blood pressure drops and breathing becomes slower
- Muscles are relaxed and blood supply to muscles increases
- Tissue growth and repair occurs
- Energy is restored
REM first occurs about 90 minutes after falling asleep and recurs about every 90 minutes, getting longer later in the night. When REM sleep takes place the following happens:
- Provides energy to brain and body
- Supports daytime performance
- Brain is active and dreams occur
- Body becomes immobile and relaxed, as muscles are turned off
- Levels of the hormone cortisol drop and increase over the night to promote alertness in morning
- The amount of sleep each night is also under homeostatic control. From the time that we wake up, the homeostatic drive for sleep accumulates, reaching its maximum in the late evening when most individuals fall asleep.
There is evidence to suggest that one sleep inducing chemical is adenosine. As long as we are awake, blood levels of adenosine rise continuously, resulting in a growing need for sleep that becomes more and more difficult to resist. Conversely, during sleep, levels of adenosine decrease, thereby reducing the need for sleep. You can find out more information at:
www.sleepfoundation.org or at www.bbc.co.uk/science/humanbody/sleep
